Process for graining ammonium nitrate



Feb. 25, 1947.'

R. c. DAjrlN PROCESS FOR GRAINING AMMONIUM NITRATE Filed June 19, 1943 frag/KEY Patented Feb. 25, 1947 PROCESS FOR GRAINING AlWMONIUM NITRATE Richard C. Datin, Petersburg, Va., assignor to The Solvay Process Company, New York, N. Y., a

corporation of New York Application June 19, 1943, Serial No. 491,558

Claims.

This invention relates to the treatment of concentrated solutions of ammonium nitrate to recover ammonium nitrate as a dry solid of desirable particle size.

The recovery of ammonium nitrate from solution by a so-called graining operation has here. tofore involved batch operations. The term graining refers to the conversion of a solution of ammonium nitrate into granular solid by evaporation of Water or cooling or both. The concentrated ammonium nitrate solution containing 1% to 5% Water, at a temperature above its salting out temperature, is run into a grainer. The standard grainer is a jacketed pan provided with a moving plow or agitator. After lling the grainer with the solution, cooling water is run through the jacket to cool and crystallize the charge. Water evaporates into the air over the grainer and it is known to increase this evaporation by passing air, which may be heated, through the material being crystallized. The cooling may be interrupted and steam introduced into the jacket to heat the material before again cooling it. The heat thus supplied increases the drying effect. Operation of these grainers has heretofore involved a period of four to six hours for cooling a solution introduced into the grainer at 120 to 160 C. to lower its temperature to 55 to 80 C. and convert it into a dry, granular product.

It is frequently desirable that grained ammonium nitrate have Well defined characteristics with respect to its particle size and bulk density. This is particularly true of ammonium nitrate to be used in the manufacture of explosives. For this purpose specifications `must be met calling for certain bulk densities and definite limits in the amounts of particles of various sizes as determined by screen analysis.

It is an object of my invention to provide a process for the graining of'ammonium nitrate wherein there is a relatively wide flexibility in adjusting conditions to produce a product of desired screen analysis and density. It is an object yof this invention to provide a process for graining ammonium nitrate solutions which may be continuously operated with a relatively small quantity of material being processed at a given moment, thus substantially reducing the explosion hazard. Further, it is an object of this invention to materially increase the production rate of an ammonium nitrate graining plant of given size.

I have discovered that large, uniformly-sized grains or crystals of ammonium nitrate are obtained when the grainingoperationis carried out at ltemperatures above 125 C. and that smaller crystals, butstill of uniform size, are obtained by graining at temperatures below 125 C. Variations in the graining temperature from to 1 or 2 below 125 C., or from 150 to 1 or 2 above 125 C., have little influence on the crystal size. I have further found that the evaporation of moisture from ammonium nitrate into air contacted therewith is greatly affected by the condition of the ammonium nitrate in contact with the air. The drying rate of a moi-st, solid ammonium nitrate may be five to ten times more rapid than the rate of drying of a slurry or solution of the ammonium nitrate.

The process of this invention utilizes these discoveries with respect to graining ammonium nitrate by mixing a concentrated solution of ammonium nitrate with a mass of crystalline ammonium nitrate which is maintained at temperatures above 125 C. or belowl25 C. during the conversion of the concentrated solution into solid, granular ammonium nitrate without permitting the temperature of the solid and` solution mixed therewith to pass through 125 C. during the graining operation. Thus, whether the process is to be used to produce a grained ammonium nitrate of relatively large particle size by maintaining temperatures above 125 C., or to produce a material of relatively small particle size by maintaining temperatures below 125 C., this temperature of 125 C. represents a limiting dividing line within the range 90 C. to 150 C. at which the graining process of this invention is carried out. This limiting temperature is not passed during the graining operation. The temperature of the materials being treated is preferably maintained within' the range to 135 C. without, however, passing through 125 -C. Whether kthe temperature is maintained above or below 125 C., will depend upon whether a coarse or fine grained product is desired.

crystallization of ammonium nitrate from the solution depends upon both the temperature ymaintained during the graining step and the water content of the solution from which the ammonium nitrate is crystallized. The ammonium nitrate is, therefore, caused to crystallize from the solutionv by evaporating water from the mixture of solution and solid in the graining step. This evaporation of water is best accomplished by passing air in contact with the mass of solid and solution. Theair is preferably preheated to to 150 C. to aid in evaporating the water.

l The mass of crystalline ammonium nitrate and concentrated solution mixed therewith is mainphase corresponds to 0.15% H2O at 90 vC. and to,

0.037% H2O ati-150. C.`y 25% liquid phase corresponds to 2.8% H2O at 90 C. Vand'to 0.4%' H250" at 150 C. For temperatures of 124 C. and 126,

C. a moisture content of 0.059% rcorresponds to 1.5% liquid phase and a moisture content of 1.1% corresponds to 25% liquid phase present in the mass of ammonium nitrate crystals in which vthe graining takes place.

The desired damp character of the mass' 'of yammonium nitrate crystals is maintained, therefore, by properly correlating the temperature and Water content of the mass so that it contains .at least 0.15% H2O at a temperature of 90 C., with this permissible lower limit decreasing to 0.03% for a temperature "of '150 1C.' and so that it contains no more than 2.8% H2O' fora temperatfurefof 90 C. with this upper limit of moisture content progressively decreasing to 1.1% H2O for temperatures of 124 C. and 126 C. and to 0.4% H2O fora temperature of 150`C. For maintaining the preferred '5% to 12% liquid phase' present, the moisture content is maintained at at least 036% H2O for 90 C., with this minimum moisture content decreasing tofu-1% H2O `for a temperature of 150 C.. and? kat no more than 1.3% H2O for a temperature of 90 C., With this maximum moisture content decreasing' to 0.5% H2O for temperatures of 12i1`'fC. and 126 C.Y and to 0.2% H2O Ifor a temperatur-e lof 150 C. 4For both the preferred vtemper'atur-e range'of 115 C, to 135 C. and preferred t'o 12% 'of liquid phase, the minimum moisture content is from 0.3% H2O for ate'mperature of 115C'. to 0.1% H2O for va temperature V'oi 135 C., and the maximum moisture contentis from 0.7% 'H2O for a temperature of 1ir5C. to -0;'3% H2O for' a temperature of 135 C.

` The correlation of moisture content and tem- 'perature Yof theV mass of crystalline ammonium nitrate in which the g'raining olf the solution takes place maybe vaccomplished by suitable control of tiren-'rate of feeding -the concentrated solution of 'ammonimn nitrate `to the mass of crystals, the rateof evaporati-n'g water into the air contacted the mass "or material by Ycontrolling the quantity and temperature Vof the air, and by suit- 'ablyrcontrolling thefra'te of heating or cooling the mass 'of crystals to which the .solution is added. l l Y l Y .Ari important 'advantage of the process of this application is that it permits producing a grained ,ammonium nitrate of desired crystal size, either vlarge or small crystals, independently of the degree to which a solution of ammonium nitrate is concentrated before it is'grained. This is a Darf ticularly desirable feature of this invention when vit is .desired to'produce 'a product of large crystal vsize by graining at temperatures above 125 C. Ammonium nitrate melts crystalli'zing at temperaturesabove 125 C. contain about 4% or less water kand about 95% or more ammonium nitrate. Such 'a solution .boils at about 180 C. Even though the evaporation is carried out under revL'ucedpressures to permit using lower temperae's,in order to avoid difficulties due to solidiion 'of the liquor in 'the vevaporator it is des1 able to 'maintain' the evaporating liquor at temperatures, substantially above, e. g.- C. or ignore, above Vits.solifl'i'c'ation temperature, This cleans 'that in 'concentrating an ammonium nitrate solution to above 96% NH4NO3 and less than 4% water, temperatures of 160 C. to 190 C. are Idesirable from the viewpoint of driving out the kwater and avoiding danger of solidication in the evaporator. ever, are approaching the temperature at which ammonium nitrate rapidly deoomposes. They present `aI real danger of explosion of the ammonium nitrate, particularly if a foreign material such as dust should get into the liquor or if t slightly higher temperatures should be accidentfrallyv attained in any part ofthe evaporator.

By the process of this invention an ammonium nitrate of desired crystal size whether large or small crystals may be produced from solutions "containing no more than 96% ammonium nitrate.

Such solutions may be prepared Without employing the high temperatures required for evaporating ammonium nitrate solutions to higher concentrations. On the other hand, if a 96% solution of ammonium Anitrate is cooled to crystallize out the salt, practical'lyxfall fdepos'its Ain the form cf` fine crystals 'at temperatures.ibelovvv l125" fC. Empioying the process of this invention, 'by maintaining a mass vof crystalline -ammonium'nitrate and concentrated solution at `temperatures above C., adding thereto ammonium nitrate solution of la concentration ino g-reaterthan 96% and evaporating water from the =hot mixture to cause crystallization fof ammonium nitrate .from the solution, the crystallization temperature is maintained abo-Ve 125 1C. vand a product in the form of relatively :large crystals is deposited from the solution. By this .mede of operation large crystal product may :be Lrecovered fromfsolution containing no more than 96% larni'nonium nitrate which 'may be preparedatrela-tively low "evaporation temperatures.

Although the process of this invention is thus particularly advantageous/when' used to recover a large-sized crystalproduct from solutions containing ;nomore than 96% ammonium nitrate, thesin-vention isl not limited to the :treatment of such solutions or Ito production of a largesized producttherefrom. 'Tjhe concentration of the solutionof ammonium ynitrate introduced to theagi-tated massA of crystal-line ammonium nitra-te may. range'Iror-n k:for exam-ple,\80% to 99% NH4NQ3 with the remainder water,.although itis .prefer-ably about-95% NI-IiNOe` and 5% water.

; The ordinary :jacketed grainers :heretofore employed in :graining ammonium nitrate*Y may be usedior'car-rying v.out thegrainingprocess of this .extendinginto the mass of material. .In treatling .a solution fed tothe graining step at a given temperature to, ,produce a product containing a given residual moisture content, the .supply of heat to or withdrawal irom the material depends upon the temperature 'of theoperation vand 4the concentration olthe ammonium nitrate -solution being supplied. For example, 'Wnenigraining at C. a solution'of l95% ammonium nitrate and containing" 02% residual moisture, 'about 12 B, t. u. of heat per pound of ammonium nitrate must be 'suppliedfto maintain `the 4desired temperature of operation;^. 'n'thefother'hand rwhen grai-mnfgat 'l 15v (C: with lthe s'ame feed s'olution These high temperatures, howabout 25 B. t. u. of heat per poundv o1' ammonium1 nitrate must be withdrawn. These heat requirements of the graining processareprincipally met.

by introducing steam or cooling water tothe jacket of the grainer. The amount of heating or cooling by the steam or cooling water thusused will also, of course, vary according to whether heat is also supplied or removed by *preheating theV air to above the graining temperature or by using air below that temperature. Y

The best results are obtainedv and it is muc 1 preferred tomaintain the mass of moist'solid ammonium nitrate into which the feed solution is introduced at substantially a constant temperature above `or below 125 C. Itis also generally desirable to remove continuously hot,y damp ammonium nitrate from the grainer to compensate for that produced from theA ammonium' nitrate solution fed thereto. Ihe materalthus removed from the grainer is then treated by a Vseparate finishing step to dry it,Y if desired, and to cool it to a temperature of about 80 C; or lower at which it will not cake when transferred to storage. However, the removal of product from the grainer maybe intermittent withoutseriously affecting the effectiveness of my process vfor the production of an ammonium nitrate product of particles of desired size and to do this much vmore economically than by the grainingprocesses heretofore known to the art.

The economic advantage and the materially lessened explosion hazard of my continuously operating process as compared with thebatch processes heretofore available .is enfiphasizedv by the following comparison. In order tol grain a 98-99% solution of ammonium nitrate inthe standard type grainers into which a charge of the solution is filled and is cooled from 150C. to l50" C. to convert it into a solid, at least six standardA grainers 6 feet in diameter are required to produce 8000 tons per year of the solid ammonium nitrate. The operation of these grainers involves having in process atv all times 3 to 6 tons ofammonium nitrate; rfh'e presence of this large quantity of ammonium nitrate in process presents a real hazard due to the tendency of the salt to explode. A graining installation of the same 8000 tons per year capacity operating in accordance with the process of this invention requires one standard grainer unit and that need only operate at about half capacity. Only 1000 pounds of am monium nitrate need be in process at a given moment; one-sixth to one-twelfth the amount present in operating the prior art processes, 'Y

The following examples further lillustrate the process of this invention.Y The procedures of these examples may be carried out in a standard jacketed graining pan provided with suitable means for passing air through the solid material being treated in the graining pan and forcontinuously supplying the ammonium nitrate solution, preferably in the form of spray to the surface of the solid in the pan. Such an apparatus, including the 'auxiliary equipment for cooling and drying the grained ammonium nitrate, is shown in the accompanying drawing.

-The apparatus of the drawing includes a jack-4 eted graining pan l provided with inlets tothe interior of the jacket for steam and cooling water. A rotatable plow 2 serves for agtating the mass of material in the graining` pan. A pipe 3', with a lower horizontal portion perforated along its bottom side, provides a means'for spraying the ammonium nitrate solution onto the contents of the graining'pan.V A plurality of pipes 4 openV ing attheir bottoml ends within the materialidgraining pan I and communicating with an air: inlet pipe 5, serve for ypassingairiinto and through` the mass .ofxmaterial being treated in the grainingpan. f

iA Water-jacketed'rnishing troughGU-is provided.. for-eolingsandddrying the grained. ammonium,

nitrate ileavingth'e graining pan throughxitsport 'l` and" introduced into the iinishing trough through van inlet 8. Trough 6 `is provided with a rotatable@` mixing screw 9 which serves to agitate the solids .introduced into the finishing trough and "to advance thematerial from the inlet end to the outlet end .of the trough containing a port l0 from which the' treated material escapes.' A suction fanfll ise'rves'V to draw air through a port I 2 into andthrough the finishing trough where it is contacted with the solid being treated therein.v4 Example 1..-340 pounds perhour of a 95 am-l moniumnitrate solution at 145 C. is continuously nium nitrate granules as grained product Awas produced from# the solution continuously fed thereto. The product removed from the grainer through outlet port 1 was subjected to a finish: ing operation in trough 6 in which it was cooled from 131 to below 85 C. and dried to about\0.1% moisture by contact with air while the product was being agitated to prevent the granules sticking Aand to give a free-flowing granular material. Screen analysis of theA productshowed about 1% retained on 10 mesh and 85% retained on 35 mesh screens. (All screen analyses given hereinare cumulative Tyler Screen sizes.)

Escample 2.-'-The above process of Example -1 was modified to feed the concentrated ammonium nitrate solution at 145 C. into a mass of granules inthe grainer maintained at 116 C, and 0.4% H2O by cooling water in the jacket of the grainer whilevair at 120 C. was forced through the mass of material at the rate `oi" 10.5 cubic feet per minute. About 168 pounds of material were continuously held in the grainer and hot; damp product of the graining operation was cooled to ,below C. and dried by contact with air. Under these conditions of operation the product hada screen analysis of about 6% lon 35 mesh and 94% 'on 100 mesh; i. e., about 88% had'particle size within the range 35 to 100 mesh,lwhereas the material grained at the higher temperature maintained in Example 1 vcontained 84% within the rrangeV 10 to35' mesh particles. l Emample 3.--A ammonium nitrate-soin# tion at 147 C. was fed into 100 pounds of grained .ammonium nitrate in a grainer'at the rate of about'o.a`% mcistur'eby suitabieccrrelanon ofthe cooling eifect of 'water introduced into the jacket of the grainer'andiof the rate and temperature of passing air through thev material. The hot;

Grained product was continuously, re-v moved lfrom the grainer at a rate such as to re-vir tain inthe grainer about 126 pounds of ammo andere damp;n..grained materiali discharged from'fthev grainer the: endflof; l: minutes was. cooled? tov below" 857 VC. anddriecl:` toffabout; 0.1% Vresidual moisture by [contactiwithainwhile':being agitated;y 'Ihe iinal product had a mesh size of 3% on.35

particlesrfwithin thesra-n'ge`r 35-` to.v 1001mesh'; Thus,

thisrproduct; produced by. a Vprocess whichjprimarily differed', from .the processi ofc Example 2 in thefrate of. feed of. theammoniumgnitrate solution .tofthemass oi ammonium nitrate granules;V y contained .somewhat lessl material within the.' Vrange'35:'to`-1T00rmesh' and-` substantially'morenes- 100-meshz size and smaller thanI the material pro'- ducedA byI the; grai'ning operation' of Example 2.

The.V graining operationl ofvthiszfinvention.'per--A formsf two't functions-LV First, it. crystallizes' the'- ammoniumfnitrate, with Lthe particular advantage;

that it'provdesa method,` for: controlling. the particle* size ofthe crystallizedv material. Secondly,l theabulk of. the Water present: in thessolutionzfed to the graining step is evaporated:simultaneously Wththe graining; The: ammonium nitrate produced. by my graining operation iszsatisfactory-for' manyfpurposes after.' being cooled with agitation lowing-in addition tofcooling the product to a.

temperature W enough: to prevent its caking;

' (1.) to remove. most of. the residual'water left intheY grained: materia'l,.` and. '('2).f rounding` the in- 'diy-idualV crystals tofincrease'rthe density'and freeflowing qualities of the product. The residual watermay beremoved togive a product with' less:

than; 0.1% residual' moisture; by treating the grainedfvmat'erialwithheated orunheatedair in a` rotary drier,. ae trough drier with screw agitator,

Y or ina standard? grainingfpann with plows or agitators tomix the materialwhile-itfis being'treated Witlrthefair'.' Byf tumbling the crystals for a sufciently lcngtimeduringr or after" the drying, they: will be polished'l or rounded; and the bulk density ofthe product-increased; Y Y

As pointed out abovc",` theprodu'ctof the grain'- ing process of this invention;whether` in the form of relatively' large or'small'particle's, is'quite uniform in particle siz'e manufacture of explosives' vsp'e'ci\':ationsv fre.- quentlyV require theproduct have` ai substantial. quantity of Vfines; i. e;,.materi"a1 of'lG mesh or smaller, and theA products. ofiV the grainin'gY and finishing'operations heretofore-describedimay not meetr somefsu'ch speciiication's. I have discovered l?articularlyforr theY avmethod fortreating'grained ammonium' nitrate Y toA modify its screen'.L analysis so that it contains more ines Without unduly modifying; the crystal sizeof the'bullcof'the material;AV Thus, a product mayf'be madef'meeting certain specifications with respect both to the quantityof iines contained have discoveredthat/by rapidly cooling grained Thisiprocedure ammonium-.nitrate fromv temperatures above 110 Y Cito-' C. or below in contact with a= solid, coldiV surface through` which a. substantialv amount of the? heaty removed in thus; coolingV theammonium 1 nitrate istransferred7 it. is possible to` convertafl substantial' proportion of the particles of the grained' ammonium'nitrate larger' than lilmeshy intoiiinesrofV a particle size suchl that they pass through@ meshi screen. This rapid cooling involves lowering the'temperature ofthe grained: Y

ammonium nitrate from above 110 Cl to below 85 C-Latfawraterof at least 0.5 C-.Vfallrin2 temperatureperminute, preferably from 0.59- to29 C. per

minute: t

The: desired increasev in iines in a grained amfmonium nitrate may be accomplished by.l introeVl ducingf hot, grained ammonium'nitrate into za.- graininggpanthrough the jacket'of which cooling'` waterV is circulated'.y The cooling by the water-- cooledisurfaces ofthe pan may be supplemented,

ify desired, bypassing cool air in. contact withthe material.

cooled graining pan containing previously cooled,` grained ammonium nitrate; The material Yis material fed to the pan. l

The treatment. of the grained ammoniumni-n trate toincrease the amountof fines containedl thereinv may be done simultaneously with agita-y tion sufficiently prolonged to accomplish the desired-rounding or polishing of. the grains andwith treatmentvof the material Vwith air lto remove residual water from thefeed= of grained arri-- moniuminitrate.v Y r l The i followingVA examples are further illustrative of` my process for graining ammonium nitrate,

solutions. and of modifying the particle sizeof thergrainednitrate by mylnishing process:

Example. 4.'-A 95% ammonium nitrate solution at 155 C. is' continuously fed onto a tumbling massI ofammonium nitrate granules containing 0.5%.;1-120"maintained=at-1329 C; in a jacketed grainer' by means .of steam introduced into'fthe jacket. TheV ammonium nitratesolution isintroduced intor the grainer'at the rate of' about 360 poundsjper hour; Simultaneously, about 16 cubic: feet perrrninute` of air'at 133' C. is-passed through the material inthe grainer to evaporate Water introduced4 with the solution; Grained ammonium nitrate-is continuously removed from the grainer'to hold the fillage of` the' latterk constant at about l-o'pounds'.-

,UnderV these; conditions' of operationfsample's of grained ;l product` leaving, thei grainer, after being. dried and cooled, show a bulk density Vof 1.2()` grams/cc.4 and a screenanalysis of 5% on lllfmesh,A 80 on 35.- meshand. 99% on 100 mesh.l

The grained ammonium nitrate as itleaves the grainer at 132V C. with a moisture content of 0.5%, HiO. is continuously. fed ata rateof` about 3.40 pounds per hour to a. jacketed, metal iinish.- ing trough. provided with. a khelicoid. screw -for mixing and advancing the material. through the trough., Cooling water at-22' Ca ispassed through the.` jacket of.v theV trough- Finished productis continuouslydischarged fromv the trough to hold aconstant tillageI of.- 260v pounds and aprocessing timeof about 48 minutes. Air. introduced at 31 C.v attherate of 220 cubic feet per minuteis passedinicountercurrent flow in contact with the mater-iat advancing: through theV trough.- -v'Ihe Similar results are obtained by feeding, the hot, grained. material into the water.'

y9 material leaves the trough at 76 C.with a moisture content of 0.074%. About half the heat removed from the grained material in cooling it to 76 C. is transferred to the cooling water through the metal trough and the other half is taken up by the air and moisture evaporated into the air. The product leaving the finishing step has a bulk density of 1.25 grams/cc. and a screen analysis of on 10 mesh, 54.5% on 35 mesh, 77.9% on 100 mesh and 22.1% fines smaller than 100 mesh.

Example 5.A coarse-grained ammonium nitrate at 130 C., having a moisture content of 0.45%, is fed toa water-cooled kettle or pan provided with a plowV agitator. .The grained ammoniuml nitrate 4is fed at the rate of 200 pounds per hour and finished product is continuously removed from the kettleI or pan'to maintain constant iillage of 198 pounds and a processing time of about one hour. Air at 35 C. is blown through the agitated m'ass to dryit to a moisture content of 0.05%. The cooling effect of the water in the kettle jacket, supplemented by that of the air, is adequate to cool the material in the kettle to a temperature of 83 C. Abouthalf the heat abstracted from the ammonium nitrate is transferred through the water-cooled kettle or pan and the other half taken up by the air and moisture evaporated. The bulk density of a product thus made lwas 1.25 grams/cc. and it had a screen analysis of 8.6% on 10 mesh. 63.3% on 35 mesh and 80 7% on 100 mesh. The bulk density of the grained ammonium nitrate before this treatment was 1.17 grams/cc. and its screen analysis was 5.9% on 10mesh, 73.7% on 35 mesh and 99.7% on 100 mesh. lin this example a grained ammonium nitrate containing 0.3% fines smaller than 10,0 mesh was converted into a product of which 19 3% was fines smaller thanv 100 mesh and of greater density than the original material.

Example 6.-'7`poundsl of coarse-grained am# moniumV nitrate at 131 C. containing 0.47% moisture is .introduced into a'iacketed finishing kettle. The batch is ,tumbled in the kettle by means of a rotating plow thereinfor 32` minutes. During this period the' material is cooled to a temperature of 80 VC."by.introducing water into the cooling jacket of the kettle andpassing air at 36 C. in contact with theL ammonium nitrate to aid in cooling it and Ato dry it. About equal amounts of lthe heatremoved in cooling the ammonium nitrate were transferred tothe cooling waterand Vto the air. I roduct thus made had a moisture content of 0.05% and density of 1.30 grams/cc. Its screen analysis showed 04% on 10 mesh, 56.1% on 35 mesh and 74% on 100 mesh.

V,Before this finishing treatment the grained amlproduct is continuously discharged to maintain a -fillage of 210pounds anda processing time of about 40 minutes. Air at lan. initial temperature of *32 C. is passed incountercurrent iiow with the material in the trough. Water at an initial temperature of 19 C. ispas'sed through the trough jacket to cool the ammonium nitrate to a temil perature of 79 C. as it leaves the trough. Product thus made had a moisture content of .05% and a bulk density of 1.25. Its screen analysis showed 2% on 10 mesh, 70% on 35 mesh and' 89.7% on 100 mesh with 10.3% i'lner than 100 mesh. Before this finishing treatment the grained ammonium nitrate had a density of 1.20 grams/cc. and screen analysis of 4.3% on .1'0 mesh, 82.4% on 35 mesh and 99.5 on 100 mesh. A material containing 0.5% fines was thus con#v Verted by the finishing treatment into a product of greaterdensity containing 10.3% fines.`

The amount of nes smaller" than 100'mesh produced by the finishing treatment described above may be varied by' varying the proportion ofcooling provided by thecool metal surfaces and the air.' A maximum amount of iines'is produced when all the cooling is accomplished by heatv transfer 'through' themetal cooling surfaces. As the' amount of heat taken'up by air passed in contact with the hot, grained ammoniumnitrate increases, the amount of fines produced decreases. It is preferred to Vprovide about half or more of the required cooling effect by heat transfer through the cool vmetal surfaces `since this gives a very desirable increase in rines. f

I claim:

l. The process forgraining ammoniumnitrate which'comprises mixing a concentrated aqueous solution of the same with a damp mass offc'rystal# line ammonium nitrate 4maintained attemperatures within one of the ranges 90 C. to 124 Cla-nd 126 C. to 150 C. during ythe graning 0f the am'- monium nitrate, vand evaporatin'g' from said mass water contained in the' solution introduced'there-1 into,whereby the ammonium nitrate 4contain-ed insaid concentrated solution is convertediintoa granular solid, the'rate. ofaddition offwater i' the solution `and the rate of evaporation' being correlated so as to maintain in the massoizcrys;

taliine'ammonium nitrate an amount of waterys'o correlated with its temperaturethatat C. said mass contains at least 0.15%' H2O with this minimum limit decreasing to-0.03% H2O for va temperature'of-l50 C., and for a temperature of 90 C. contains no morethan 2.8% H2O with thisY maximum limit decreasingito no morethan 1.1% H2O for temperatures o'f 124 C. and 1267i C. and to no more than 0.4% H2O for -a temperatura'of 2. The process forgraining ammonium nitrate which comprises `mixing "ai concentrated. aqueous solution of the same-with a damp massfof crystal= lineammonium nitrate maintained 'at temperatures within zone of`the"ranges'115 C. to,124-C. and 126 C. to 135;C. during the graining of ltlie rammonium nitrate, and evaporating water-con'- tained'in said'solution 'into air in contact with l the mass of crystalline ammonium nitrat'with which thesol'ution is mixed, whereby the anirnonium nitrate contained in said concentrated 'solution is converted. intoV a" granularsoli'd, the rate' of addition lof' water in the. solution andthe rate of evaporation being correlated "asoasg-to maintain in the mass of crystallinela'mmon'ium nitrate an amount'o'f 'waterso correlated with the temperature that 'at 115 C: said 4masscon- 'tains at least 0.3% H'zO'vwith thislowerflimitzin l solution.

centrated aqueous Vsolutionfjof ammonium nitrate into a` damp mass of crystalline ammonium nitrate fand mixing the solution .therewith While maintaining the mass vat temperatures Within i i one of :the Aranges '19.0 '.C. to .124 C. and 126 C. to s 150 C., simultaneously with .the mixing of 4said solution'and dampmass oi-fcrystalline ammonium nitrate, passing preheated airthrough and y.in-intimateiconta'ctwith the damp mass to :evaporate into i the :air .waterrcontained in `.the .concentrated aqueous .solutir'm1 thereby converting Athe ams monium :nitrate .contained insaid .concentrated solution-into a granular solid, lthe `rate .oi addiin ftheamassnficrystalline ammonium nitrate an a'lnount of residual unevaporated watervgso cor- 'related-with :the temperature :at which themass which zcomprises :continuously introducing a'con-V .evaporation fbeing correlated aso as '.to maintain than 0.4% `-I-IzO :forza temperature Aoi 150 Cl, and

1 withdrawing thus grained ammonium nitrate fromsaid mass fin amount corresponding to the ammonium nitrate introduced in 1said aqueous v4.y The'process for fgrainingammonium nitrate which comprises continuously introducing a concentrated aqueous solution iof 'ammonium nitrate into a 'damp mass of crystalline ammonium` nitrate and mixing 'the solution therewith while v maintainingthe 'mass at 'a :substantially constant s temperature within 'one of itheranges '90 to 124 C. and k126 to 150 c., simultaneously with-the' mixing fof said Xsolution'and damp mass of crystalline ammonium nitrate, "passing 4preheated lair through and fin :intimate contact With 'the .damp mass to l'evaporate linto the air Water :contained in lthe concentrated aqueous solution, lthereby 'conyerting' the ammonium rnitrate contained in f' said lconcentrated solution finto a granular solid,

fthe rate of 4addition of waterinthe solution `and the lfrate of evaporation 'being Acorrelated v'so as to .maintain inthe -ma'ss of crystalline ammonium nitrate ian :amount of residual 'unevaporated water so correlated with the temperature Vat which the mass 'is maintained that "at'90 C. said mass :contains at leastj'0.6% H2O -with'this lower 'limit 'in the :amount-'of vwater decreasing :to 053% lH'OV for a ytemperature o'f '115 C. *and tto.0:1"%v H2O V`for -temperatures :'of :135 1C. to .150 and :tor .la temperature of" C. contains no more than v1.3% 'H2O with tliiszmaximum amount Yof 'water'decreasingf'to 0.7% yH20 ffor :a'temperature of *115 `to 0.5% :H2O for temperatures Yof 124 Cnand .126 Gto 0.31%'H2O for :a temperature of '135 C. :and toj;0.2'% .i1-I2@ foratemperature .of 150 C., :and withdrawing fthusllgrained ammonium n :nitrate from tsaid `mass in amount .corresponding tocthe fammonium nitrate introduced in lvsaid i5. The l.process 4vfor ;gralriing ammonium nitrate to produce :azproduct Tof .large crystal :size @which l comprises .mixing a. concentrated vaqueous.solu- .ftiongof ammonium 'nitrate containing no -more monium nitrate with which thesolution'isl mixed; the rate of additionof water in the solution .and therateof evaporation being correlated f'so as to maintain in said mass -an amount `of vWater so correlated with its temperature that at 126 VC. sadnmass containsfat least 0.05% H2O with :this minimum limit decreasing to y0.03% H2O :for a temperature `of 15.0 C., and for atemperature v.ci 112.6 C. contains :no more than 1.11% H2O with this maximum limit :decreasing to no `more than 0.4% H2O for a temperature of 15.0 -.C. :whereby the ammonium mit-rate contained kin .said concentrated :solution is .converted into sa. granular solid of large crystal-size. y6. .Theprocess for producing a grained am .monium .nitrate :from `a `concen-,tralicci solution of the same which comprises mixing said concentrated-.solution :withia 4damn mass :of crystalline ammonium nitrate maintained at temperatures Within .one of'the:ranges,115o Carto :124 and 126 -.C. Vto 135 C. l.during the .graining 'of .the ammonium nitrate, .feyaporating Water contained in said solution into air :in-.contact with .the mass or crystalline `annnoniuin nitrate, `whereby the ammonium nitrate containedfin said ,concentrated solutionv is converted .into .faigr-anular solid, the rate of addition of Water in the .solution .and the .rate .of r4eva-poration being-correlated so as tonnaintain .in-.the .mass of Ldamp crystalline ammonium v.nitrate Ean amount .of water so correlated with thetemperatureyof the damp .mass vthat at -.l15C.1'said -'ma ss..contains at `least 0.3% .with ythis lewe-r limit in the `amount ,.of water .decreasing to v0.1% H2O Vfor ra .temperature of C.. and for a temperature of .115 .Cl con.-

tains no more-than O;7% .HzOwith this maximum amount of water decreasing to,.0.j3% HQO for a temperature of .135 .C.., withdrawing from .said mass -.-hot, damp. #grained` ammonium :nitrate yat Va temperaturewithin .the ,range .115 .to 135 C.

and :cooling `.the .thus liilthdrfawn material by contact .with `cold, L`s.olic'i.heat transfer surfaces 1Whileagitating thematerial and .cooling .the-.hot vgrained `ammonium l'nitrate to ,a *temperature not above ,859 -.C...at ..a ,rate .of -at `least -0.1.3913. 4fall in ktern-peratureY per vminute 1 with a .substantial .aalmountlof thelieatabstractedin thus cooling the ammonium nitrate .being removed through said Lcoolingsurfaces. l .s

The -iprocess .for-.producing Vgrained ammonium .-nitratei rom aaconcentrated solution. of V.thc same which comprises .continuously introducing fa .concentrated aqueous solution of ammonium .nitrate into `a damnmassof .crystalline .ammo- .fnium ynitrateand mixing the solution ,therewith while maintaining .the .mass at a .substantially .constant .temperature within :one .of ,the ranges 00 to 124 -C.1and :126 to 15.0 C., feyanorating water contained .in said solution into .air .in .Con- -tact .with the .mass .of .crystalline :ammonium vnitrate with .which the solution .-mixed, where- 'zbyithe {ammonium-nitratecontained in :said ,con-

'centrxated solution V(is f vconverted into a .granular solid-the frate fof-addition Tcif water fin Athe solution .and the ,irate lof- .evaporation .being .-,correlated so of 150 C., continuously withdrawing hot, damp ammonium nitrate from the aforesaid mass of crystalline ammonium nitrate, agitating the thus Withdrawn material while passing air "therethrough to evaporate Water therefrom and while cooling the agitated material by contact with cold, metal heat transfer surfaces maintained at a temperature at which the hot grained ammonium nitrate is cooled to not above 85 C at a rate of 0.5 to 2.0 C. fall in temperature per minute by transfer of heat from the hot grained ammonium nitrate through said metal surfaces supplemented by the cooling effect of the air and eva-poration of Water thereinto.

8. The process for finishing grained ammonium nitrate to increase the quantity of fines therein which comprises agitating a mass of hot grained ammonium nitrate initially at a temperatureabove 110 C. While the mass of agitated grained solid is in contact with cold, solid heat transfer surfaces, and cooling said hot grained ammonium nitrate from above 110 C. to not above 85 C. at

a rate of at least 0.5 C. fall in temperature per minute with a substantial amount of the heat abstracted from the hot grained ammonium nitrate in thus cooling it being removed through said cooling surfaces.

9. The process for iinishing grained ammonium nitrate to increase the quantity of fines therein which comprises agitating a mass of hot grained ammonium nitrate initially at a temperature above 110 C. while the mass of agitated grained solid is in contact with cold. metal surfaces, and cooling said hot grained ammonium nitrate from above 110 C. to not above 85 C. at a rate of 0.5 to 2.0 C.- fall in temperature per minute, with at least half the heat abstracted from the hot grained ammonium nitrate in thus cooling it being removed through said cooling surfaces.

10. The process for finishing grained ammonium nitrate to increase the quantity of iines therein which 'comprises agitating a mass of grained ammonium nitrate and repeatedly bringing the agitated material into contact with cold metal surfaces, continuously introducing into the mass of thus agitated material hot grained ammonium nitrate initially at a temperature above 110 C., cooling said agitated mass at a rate so correlated with the rate at which the hot grained ammonium nitrate is introduced intothe agitated mass that said mass is maintained yat a temperature not above C. and theentering hot grained ammonium nitrate is cooled to a. temperature not above 85 C. with 0.5 to 2.0 C. fall in `temperature per minute, said cold metal surfaces removing a substantial part of the heat contained in the hot grained ammonium nitrate.

RICHARD C. DATIN.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,661,203 Toniolo Mar. 6, 1928 1,721,798 Toniolo July 23, 1929 1,131,361 Gallup Mar. 9, 1915 FOREIGN PATENTS Number Country Date 301,496 British Oct. 17, 1929 

